Medical devices may be coated so that the surfaces of such devices have desired properties or effects. For example, it may be useful to coat medical devices to provide for the localized delivery of therapeutic agents to target locations within the body, such as to treat localized disease (e.g., heart disease) or occluded body lumens. Localized drug delivery may avoid some of the problems of systemic drug administration, which may be accompanied by unwanted effects on parts of the body which are not to be treated. Additionally, treatment of the afflicted part of the body may require a high concentration of therapeutic agent that may not be achievable by systemic administration. Localized drug delivery may be achieved, for example, by coating balloon catheters, stents and the like with a therapeutic agent to be locally delivered. The coating on medical devices may provide for controlled release, which may include long-term or sustained release, of a bioactive material. Coatings can be applied to medical devices by processes such as dipping, spraying, vapor deposition, plasma polymerization, spin-coating and electrodeposition.
Aside from facilitating localized drug delivery, medical devices may be coated with materials to provide beneficial surface properties. For example, medical devices are often coated with radiopaque materials to allow for fluoroscopic visualization while placed in the body. It is also useful to coat certain devices to achieve enhanced biocompatibility and to improve surface properties such as lubriciousness.
A conventional self-expandable (SE) stent has an expanded form when not constrained. To deliver the stent to the desired location in the body, the stent typically is compressed radially and loaded into a delivery system. A typical delivery system consists of an outer tubular sheath retaining the compressed stent. The delivery system is tracked to the region of a vessel being stented. The stent is then released from its compressed state by retracting the sheath and/or pushing the stent out of the sheath. When released from the constraint of the sheath, the stent self-expands back to its expanded form to scaffold the vessel wall.